The present invention relates to a method for prilling sulfur. More particularly, this invention relates to a method for preparing hard beads or prills of elemental sulfur.
Sulfur is one of the essential elements needed for plant life. In many areas of the world, there is an insufficient amount of sulfur in the soil to adequately support plant life. Moreover, in alkaline soils, sulfur is not only needed to support plant life, but is also required as a soil supplement. As a soil supplement, sulfur increases the water intake and aeration of the soil, improves the physical conditions of the soil, eliminates the harmful alkalinity and sodium problems of the soil, and increases the availability of certain nutrients and elements for plant growth and life.
Elemental sulfur can be added to the soil in many forms such as: the sulfate form, e.g. calcium sulfate; the sulfide form, e.g. ammonium sulfide or calcium sulfide, elemental sulfur and the like. Elemental sulfur is preferred because it is oxidized in the soil by microorganisms to a form which is the desirable form for plant nutrition and soil improvement.
Elemental sulfur is available in many forms, such as pellets, flake sulfur, ground sulfur, finely powdered sulfur and the like. Finely powdered sulfur is rarely used because it is difficult to handle and easily becomes air born to form dust clouds. Sulfur dust is very irritating to the lungs of both man and animal and presents an explosive hazard.
Flake sulfur contains a large percentage of water and is easily broken up during transportation and handling creating dust fines which are easily air born. Ground sulfur is also difficult to handle and tends to powder upon handling and during transportation. Prilled or pellet sulfur is an improvement over the above forms of sulfur; however, the prilled or pellet sulfur formed by the conventional methods contains a high percentage of water, is somewhat friable and is easily broken up during transport and handling creating dust fines, and is not uniform in size.
The present invention provides a method for producing prilled sulfur which has a low percentage of water, is durable and not readily friable and, is of uniform size.
Many attempts have been made in the prior art to produce a prilled sulfur having properties of the prilled sulfur produced by the present invention without success. For example, the Perry U.S. Pat. No. 1,285,358 discloses a process for the preparation of globules which comprises spraying molten sulfur into air wherein small globular bodies of sulfur are formed. The Bacon et al. U.S. Pat. No. 1,378,084 and the Campbell U.S. Pat. No. 3,334,159 both disclose somewhat similar methods for prilling sulfur. These methods consist of allowing molten sulfur to drop through a perforated plate to form droplets or shot like bodies of sulfur which are immediately immersed in a cool aqueous solution to solidify the molten sulfur shot. These processes produce sulfur pellets of non-uniform size, containing a high water content. The Nashner et al. U.S. Pat. No. 3,034,864 and the Landucci et al. U.S. Pat. No. 3,484,201 disclose a method for preparing sulfur prills from sulfides. Metal sulfides are oxidized to form molten elemental sulfur globules in an aqueous sulfuric acid slurry. The slurry is cooled to solidify the sulfur globules. These processes yield sulfur pellets of non-uniform size, contaminated with water and/or other impurities. The Canadian Pat. No. 824,608 (issued Oct. 7, 1969) discloses a method for prilling sulfur by spraying molten sulfur out of a gun. The sulfur spray is cooled with steam and/or water to solidify the sulfur pellets which fall to the ground and are collected. This process has been commercially used and produced sulfur pellets having fairly good handling characteristics, but the pellets are not particularly uniform in size. The British Pat. No. 763,936, published Dec. 19, 1956 discloses a variant of the Nashner et al. and Landucci et al. process described above. The British process consists of dispersing impure sulfur in an aqueous sulfuric acid at temperatures exceeding the melting point of sulfur to agglomerate the sulfur into pellets. The molten pellets are separated from the slurry and dispersed in water containing a surfactant for the sulfur impurities. The water is heated to a temperature in excess of the melting point of sulfur to obtain agglomeration and then is cooled to below the melting point of the sulfur to solidify the sulfur globules. The process disclosed in British Pat. No. 1,001,486 is a variant of the above process. In this process, molten sulfur is dispersed in an aqueous medium to form molten sulfur globules. The sulfur globules are then cooled to form solid discrete particles of sulfur which are separated from the aqueous medium. In all the above processes wherein the sulfur pellets are formed in an aqueous medium and solidified therein, the resulting pellets contain a fair quantity of water and the other impurities contained in the aqueous medium.